This invention relates to nanostructure arrays for multifunctional surfaces that are mechanically robust and provide superior optical and wetting properties such as antireflection and superhydrophobicity/hydrophilicity. The invention also relates to the fabrication process for the nanostructure arrays.
Nanostructured surfaces have been widely studies for their superior optical and wetting properties such as antireflection and superhydrophobicity/hydrophilicity [1, 2, 3]. Due to subwavelength feature size, nanostructured surfaces behave as an effective medium with gradually varying index of refraction. Such a surface can be used to suppress Fresnel reflection at material interfaces, thereby acting as an anti-reflection surface and allowing broadband light to pass through without reflection loses [4]. In addition, both hierarchical roughness of these structures and an intrinsic chemical property of the surfaces can induce artificial superhydrophobicity or superhydrophilicity, which can be applied as self-cleaning or anti-fogging surfaces, respectively [5, 6].
Recently, high aspect ratio (approximately 5) silica nanocone structures, demonstrating structural superhydrophilicity or, in combination with a suitable chemical coating, robust superhydrophobicity, and enhanced transmissivity, have been successfully fabricated directly on a fused silica substrate with few defects and a large pattern area [7]. By using interference lithography and multiple shrinking mask etching, the desired aspect ratio nanocone structures were created for optimizing the multifunctionality of the textured surface [8]. Although the prior art structures provided notable performance, the mechanical stability and properties of these prior art structures are not suitable to sustain mechanical impact (including finger touch) because of the high aspect ratio and isolated nature of the structures.
It is an object of the present invention to provide an alternative type of nanostructure for multifunctional surfaces (anti-reflectivity, superhydrophobicity, superhydrophilicity and superoleophobicity) with high mechanical strength and high optical and wetting performance compared to existing nanostructures [7]. Another object of the invention is a fabrication process for the structures disclosed herein that is simple, and cost effective for manufacturing the multifunctional surfaces.